The present invention relates to a washer and screw fastener assembly, wherein the washer is held captive thereon; and more specifically, to a preassembled washer and screw assembly of the type employed to provide an electrical terminal for appliances, or the like.
It is relatively common practice to employ preassembled screw fasteners and washers as electrical terminals in numerous types of assemblies such as telephones, household appliances and television sets, wherein the terminals are used for attaching lead wires and/or antenna wires. In this regard the conductive elements, such as metal terminals crimped onto the end of lead or antenna wires, are positioned beneath the captive washer, and the fastener is then seated to bring the washer into clamping engagement with the terminal. In practice, the threaded fastening device, or the surface against which the lead wire is engaged is in conducting relationship with the interior circuitry of the device. Generally, the type of washer employed is that which includes an axially extending peripheral flange, which in many instances is serrated to enhance the gripping or clamping contact.
These terminal assemblies are generally of the "Sems" type, in that the washer is held captive upon the screw fastener by the screw thread or some other structural configuration of the fastener, which is formed on the fastener blank subsequent to assembly of the washer thereon.
While Sems type assemblies have been employed for a considerable time as terminals, they are generally of the type as shown in FIG. 1 of the drawings, and as such possess certain inherent disadvantages. As these prior art assemblies normally employ a washer having an axially extending peripheral flange, the engagement of the thread forming dies with the shank of the fastener is limited by the axially projecting flange. As will be explained more fully hereinafter with regard to the detailed description of the prior art and the present invention, this fact results in a relatively long unthreaded section which permits considerable relative movement or "play" between the washer and the screw shank. Keeping in mind that terminals are normally employed in a vertical orientation, the extent to which the screw fastener must be backed out of a mating aperture, in order to raise the washer sufficiently to allow for positioning of the terminal beneath the washer, is increased by the degree of play or relative movement between the washer and the shank. That is to say, the retracting movement of the fastener must overcome this play, before the washer is elevated above the adjacent supporting surface. As such, there exists the distinct possibility that the fastener may be backed completely out of the aperture, which will require re-engagement and loss of assembly time. Also, the amount of movement of the screw fastener relative to a threaded aperture required in the operation is considerable and can effect the overall assembly time; which is significant since numerous such assembly operations must be performed. The present invention eliminates, or at least materially reduces these disadvantages.
More specifically, with the present invention the washer is provided with an intermediate portion about the central aperture that includes an inwardly and downwardly tapered segment, which may take the form of a generally frusto-conical configuration. The net effect of this, is that the central aperture is moved axially toward the plane of the edge of the axially extending flange, and away from the plane of the upper portion of the washer. Thus, as will be apparent from a comparison of FIGS. 1 and 2 and the discussion to follow, the play between the washer and the fastener is materially reduced. Accordingly, upon retractive movement of the fastener, elevation of the washer in relation to the adjacent supporting surface will take place almost immediately.
The present invention is possessed with numerous other objects, advantages and features which will become apparent to those skilled in the art from the hereinafter presented detailed description of the illustrated embodiment, taken in conjunction with the drawings.